Distribution of an EP Film on Wear Surfaces

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Abstract
A new method has been developed for the determination of the distribution of EP film components on irregularly-shaped wear surfaces. It entailed the use of data from radiotracer counting, autoradiographic analysis, densitometer tracings and numerical integration. The method has been applied in a study of the film formed on engine valve train parts run in an oil containing zinc dialkyl dithiophosphate tagged with radioactive sulfur. The technique is applicable to similar investigations with other additives. The result obtained showed not only how much film was formed on wear surfaces by the additive, but it also pin-pointed areas on the mating parts, where the EP film concentrated. This type of information was not obtainable by other means. In runs made with a cam and tappet tester, the amount of sulfur film found on various valve train parts decreased in the following order; cam nose, center tappet area and cam flat. For the same area on the tappet, activity was greater for phosphate-coated parts than for untreated parts. Preliminary results indicated that it was possible to relate contact pressure experienced by the mating surfaces fairly precisely with the amount of EP film formed.